If we ever make contact with an alien species, it will be the greatest event in our history. Despite numerous reported sightings, testimonies of abductions, film footage and photographs, there still remains no firm evidence that we have ever had any genuine contact with extraterrestrials.
This isn't to say that we won't at some point in our future actually make contact. However, if contact was to be made, it would probably involve them coming to us, rather than us travelling to them. Our technology is no way near sophisticated enough for us to travel the required distances to take us to potentially habitable planets. Alien technology might provide the necessary nohow.
There still remains the possibility that they have already made the journey. If this is the case, then the obvious question that needs to be asked is why they have not made confirmed contact and attempted to communicate with us. Whilst scientists theorise an answer to this question, claiming that we are mere primitive barbarians in comparison to them and they are just playing with us in the same manner as a child would an ants' nest, I have an alternative theory.
If you consider are early attempts to conquer space, and even some of the more recent launches from new countries joining the space race, they often involved sending rockets up containing animals. These space craft frequently fail to return to Earth. Consequently, space is littered with space capsules containing the decaying remains of animals. Should any alien species encounter one of these whilst journeying to our planet, they would no doubt open it up and perform a few tests on the contents. The assumption could easily be made that either dogs or monkeys are the dominant species on our planet. Hence any contact would reap little reward for them. They would probably just dump the contents of their space toilet and set course for home.